1. Field of the Invention
This invention relates generally to the field of loudspeaker enclosures and in particular, to light-weight, high-power thermally stabilized speakers.
2. Prior Art
High-power speakers as known in the art have a number of serious deficiencies, which stem from typical speaker construction. The problems are especially acute in those large speakers intended for use with portable, but high-powered sound systems, for example those used by bands and singers on tour. The term loudspeaker will be used herein to denote an electroacoustical component of a speaker, speakers including one or more loudspeakers, cross-over controls, and the like.
A typical speaker construction is illustrated in FIG. 1. A speaker 2 comprises a box-like enclosure 3 formed by six sides 4. Such a box is typically constructed from thirteen ply baltic birch plywood using heavy internal bracing, wood glue and an enormous quantity of wood screws. The box encloses one or more loudspeaker 6, each loudspeaker comprising a magnet assembly 8, an electromechanical driver/voice coil (not shown) and a horn 10. The magnet assembly (comprising magnetic and steel parts) 8 is very heavy, and a heavy-duty loudspeaker frame is usually required. Often, the horn forms part of the frame and is provided with a flange 12 by which the loudspeaker is affixed to what is thereby defined as the front panel of the speaker. The magnet assemblies 8 are typically the heaviest part of the loudspeaker, and the horn 10 and/or the frame must be of sufficient strength to support the magnet assembly. The box itself must be of sufficient strength not only to support the entire loudspeaker, but to support its own weight as well, through rigging fixtures or hardware 14. Such speakers, commonly referred to as "touring boxes", must be constructed by skilled cabinet makers, in order to assure that the speakers will withstand the rigors of transit and rigging. A consequence of operating high-powered loudspeakers is the generation of considerable thermal energy in and by the large and heavy magnet assemblies. The robust and closed construction of typical touring boxes results in very high ambient operating temperatures within the boxes. Operating temperatures within the box are normally on the order of approximately 150 degrees F.
The box must also perform an acoustical function, namely providing a rigid enclosure for the loudspeakers to enable efficient sound amplification and transmission. As a result, typical touring boxes weight in excess of two hundred fifty to four hundred pounds. Such touring boxes are not only expensive to manufacture and thermally inefficient to operate, but are extremely difficult to transport and rig.
No advances to speak of have been made in reducing the weight of the enclosure box, it being accepted by those skilled in the art that such heavy and robust construction is necessary to support the loudspeaker, although Japanese Patent No. 58-12498 is of some interest. However, there have been some efforts made to more efficiently dissipate thermal energy from loudspeakers and loudspeaker voice coils. Such efforts are exemplified by U.S. Pat. Nos. 3,991,286; 4,138,593; and, 4,210,778.
The above-noted Japanese patent discloses a speaker wherein the loudspeaker is supported by means of the magnet assembly, rather than the horn. This reduces the need for a heavy-duty loudspeaker frame. However, the reference does not disclose any heat transfer techniques and uses a conventional heavy-duty, heavy weight enclosure or box. Moreover, the injection molded plastic construction has very low strength. In the heat dissipation device for a loudspeaker voice coil disclosed in U.S. Pat. No. 3,991,286 the coil form for a loudspeaker voice coil is made of a material having high thermal conductivity. The coil form is attached to or integrally formed with a highly thermally conductive spider member which resiliently supports the coil form on the frame structure of the speaker, which also has high thermal conductivity. A heat sink member to facilitate the dissipation of the thermal energy is attached to the speaker frame structure. Construction of the speaker is otherwise conventional.
The moving voice coil loudspeaker with heat dissipating enclosure disclosed in U.S. Pat. No. 4,138,593 comprises the speaker housing or a surface portion thereof and/or the speaker sound panel or sound wall or certain surface portion thereof being formed by a material having a high thermal conductivity, the moving-coil unit of the loudspeaker being in thermally conductive engagement with the thermally conductive material. The construction is otherwise conventional. The loudspeaker system disclosed in U.S. Pat. No. 4,210,778 utilizes a heat pipe for conducting thermal energy from the loudspeaker, the heat pipe having a reflux port or other exit in a side of the enclosure for shedding the thermal energy. As with the other references, the construction of the box is fully conventional.
The inefficiencies of prior art touring boxes appear to stem from a firm belief by those skilled in the art that the enclosure must not only be sufficiently rigid to provide for proper acoustical response, but must be of sufficient strength to support not only its own weight, but the weight of the loudspeakers and any other equipment disposed therein or thereon. It is often desirable to place additional electronic amplifiers in close proximity to such speakers. A popular amplifier is the Carver Model PM 2.0 which develops 1000 watts of amplification and weighs only ten pounds. Despite its light weight, heat dissipation remains a serious problem. The invention taught herein overcomes all of the problems known with the prior art, by recognizing that the enclosure need in fact provide only one function, namely providing a rigid enclosure for the loudspeakers to assure proper acoustical response. This is accomplished by mounting one or more loudspeakers to a principal load-bearing member by means of the magnet assemblies of the loudspeakers, the load-bearing member exhibiting good thermal conductivity. Rigging or mounting of the loudspeaker and enclosure can be by attachment to the load-bearing member. The enclosure comprises walls formed of a rigid light-weight material which is also mounted on th load-bearing member, so as to enclose the one or more loudspeakers. The assembly is easily moved and mounted and thermal energy generated by operation of the loudspeakers is effectively dissipated through the load-bearing member. Overheating is avoided even when electronic amplifiers are also mounted in the speaker, as they can also be mounted on the load-bearing member, in thermal engagement therewith. The overall savings in weight can be as much as seventy percent, or more.
A number of advantages result form this design. In a conventional speaker, the wood box must be strong enought to support its own weight as well as the weight of all components mounted thereon and therein, by means of brackets or the like affixed to the sides thereof. The enclosure of a speaker recording to this invention need only be strong enough for acoustical purposes, that is, it need only be sufficiently strong or robust to be rigid. The enclosure of a speaker according to this invention has no load-bearing responsibility whatsoever, except for its own weight. A loudspeaker box according to conventional practice must do two jobs, acoustical response and component support. The enclosure of a speaker according to this invention need fulfill only an acoustical job. Most prior art speakers, notwithstanding those in the patent references discussed above, make no provision for heat transfer. Speakers according to this invention provide for full dissipation of excess thermal energy, including such additional components as amplifiers.
The very heavy weight of prior art speakers requires extra heavy-duty hanging hardware and extra heavy-duty speaker coverings. The very light weight of speakers according to this invention not only facilitates easy handling and transportion, but enables the use of lightweight hanging hardware and enables speakers to be more easily and conveniently stacked on one another. The lighter weight also enables use of lighter protective coverings, as there is less weight due to the speaker when impacted or impacting other objects. In fact, hanging hardware is not even strictly necessary, as speakers according to this invention are so light in weight as to enable full rigging by simply using cages or cargo nets. Speakers are usually suspended over the performers, or audience or both. Speakers according to this invention provide much higher safety margins against rigging failure.
Speaker enclosures made in accordance with the prior art require the skills and expense of experienced carpenters or cabinet makers, whereas speakers according to this invention may be assembled with simple tools and without the need for skilled craftsman.
Finally, prior art speakers require that components, particularly loudspeakers comprising magnet assemblies, electromechanical drivers and horns, must have supporting frames or be of sufficiently robust construction to be self-supporting. In speakers according to this invention, the loudspeaker assemblies can be affixed to the load-bearing member by means of the magnet assembly, which is the single heaviest part of the loudspeaker. No frames or particularly robust construction is otherwise required.